The Proposed studies are designed to provide information about the mechanisms and physiological significance of interactions among serotonin (5-HT) receptors in the control of female rat lordosis behavior. Emphasis is placed on 5-HT's role in the mediobasal hypothalamus (MBH), especially the ventromedial nucleus of the hypothalamus (VMN). The specific aims of the present application are to identify mechanisms responsible for this interaction. Studies are also designed to test the hypothesis that 5-HT's dual function within the VMN enables the organism to modulate its behavioral repertoire in a manner conducive to both species and individual survival. The specific aims of the proposed studies are: To determine the relative distribution of 5-HT1A, 5-HT2A and 5-HT2C receptors within the VMN of proestrous rats and of hormonally-primed, ovariectomized rats. To test intracellular mechanisms responsible for the effects of 5-HT1A and 5-HT2A/2C receptors. Experiments are proposed to test the hypothesis that 5-HT1A receptor-mediated inhibition of cAMP accumulation is involved in the receptor's inhibitory effect on lordosis behavior and that inhibition of cAMP accumulation is involved in the receptor's inibitory effect on lordosis behavior and that 5-HT2 receptors attenuate this inhibition through actions involving protein kinase C. Experiments are proposed to test the hypothesis that 5-HT1A receptors reduce the release of norepinephrine (NE) and that 5-HT2 receptors enhance the release of gamma-aminobutyric acid (GABA); and that these effects of 5-HT on NE and/or GABA contribute to 5-HT's ability to both inhibit and facilitate lordosis behavior. To test a model about the physiological significance of 5-HT's dual role in the control of lordosis behavior. Experiments are designed to evaluate the hypothesis that 5-HT2 receptors reduce inhibition of lordosis behavior (mediated via 5-HT1A receptors) that is initiated by environmental challenge.